Valve stem and method of manufacture; improved stem packing

ABSTRACT

A valve stem has a thickness of hardfaced material on its outer diameter in the area contacting the stem packing where the seal is formed which prevents corrosion, erosion and/or scratching of the valve stem, thereby preventing formation of leak paths. A valve packing comprises a vertically stacked array comprising alternating metal pressure rings and graphite seals.

TECHNICAL FIELD

[0001] The present invention relates generally to valves of the typeused in the petrochemical, refining, and other industries, and moreparticularly to an improved valve stem which is resistant to chemicaland mechanical deterioration, to a method of manufacturing the valvestem, and to an improved packing construction useful in conjunction withthe valve stem.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] Perhaps the most common valves used in the petrochemical,refining, and other industries are gate valves. Major components of gatevalves include body, a valve stem, a sealing member, and seat ringswhich are engaged by the sealing member to close the valve. Because thevalve stem must extend from inside the valve body to outside the body, astem packing must be installed to effectively seal between the body andthe valve stem, thereby containing the product inside the piping systemof which the valve is a part. To achieve the necessary dynamic seal toboth contain the product within the piping system and allow the valvestem to actuate up and down, the area of the valve stem which makescontact with the stem packing must be smooth, round and have no taper onthe outside surface of the valve stem.

[0003] When the valve is new, the foregoing conditions are met andproduct inside the piping system is prevented from leaking to theoutside. As the valve ages, chemical corrosion from the product,galvanic corrosion from the packing, and erosion and corrosion fromatmospheric conditions all combine to reduce the smoothness of the valvestem that is necessary to maintain the seal. Also, roughness of thevalve stem can occur as the valve stem is pulled through the stempacking during normal cycling due to abrasive materials accumulatingbetween the valve stem and the seal. Any of these factors, andparticularly combinations thereof, can result in leak paths beingcreated and leakage to occur. This is unsatisfactory for numerousreasons, the most important of which involves increasing enforcement ofthe federal Clean Air Act which makes prevention of leakage or “fugitiveemissions” essential.

[0004] Previous attempts at solving the foregoing problems have includedthe application of the material sold under the trademark “HASTALLOY”®.Such material is partially effective in slowing valve stem deteriorationdue to chemical attack but is ineffective as to mechanical degradationof the valve stem surface.

[0005] While the prior art discloses a variety of valves, no priordisclosure shows a device where leakage is prevented by way of anoverlay on the valve stem in the area of the stem packing. The improvedvalve stem of the present invention departs from the design of priorvalve stems, and in doing so, provides a valve which prevents leakageand fugitive emissions as the valve ages.

SUMMARY OF THE INVENTION

[0006] The present invention provides an improved valve in which thevalve stem has an overlay of hardfaced material that reduces thedeterioration of the stem packing sealing surface. The hardfaced overlayis constructed of materials which resist corrosion, erosion, andscratching, thus eliminating the cause of most defects in the sealingsurface of the valve stem. This in turn allows maintaining the originalpacking area finish, thereby preventing the creation of leak pathsthrough the stem packing and fugitive emissions from the valve.

[0007] In accordance with more specific aspects of the invention, theportion of the valve stem that engages the sealing material has anominal outside diameter which is first reduced, either duringmanufacture or modification of the valve stem. Hardfaced material isapplied to the reduced diameter portion of the valve stem until thediameter thereof is increased beyond the nominal size. The diameter ofthe hardfaced material is next reduced to the nominal size, thusproviding a valve stem that is smooth, hard, and resistant to chemicaland mechanical deterioration.

[0008] The invention further comprises an improved valve packing usefulin conjunction with the valve stem. The improved valve packing comprisesalternating metal pressure rings and graphite seals. The improvedpacking enhances the performance of the improved valve stem bypreventing leak paths through the packing which would otherwise resultin fugitive emissions.

BRIEF DESCRIPTION OF DRAWINGS

[0009] A more complete understanding of the invention may be had byreference to the following Detailed Description when taken inconjunction with the accompanying Drawings, in which:

[0010]FIG. 1 is a sectional view of a gate valve having a valve stemconstructed in accordance with the invention;

[0011]FIG. 2 is a side view of the improved valve stem of the invention;

[0012]FIG. 3 is a cross-sectional view of the valve stem of FIG. 2;

[0013]FIG. 4 is an illustration of a first step in the method of theinvention;

[0014]FIG. 5 is an illustration of a later step in the method of theinvention;

[0015]FIG. 6 is an illustration of a still later step in the method ofthe invention;

[0016]FIG. 7 is a sectional view of an improved valve packing useful inconjunction with the improved valve stem illustrated in FIGS. 1-6,inclusive;

[0017]FIG. 8 is an illustration similar to FIG. 7 showing a differentapplication of the improved valve stem packing;

[0018]FIG. 9 is an illustration of a packing similar to that of FIG. 7but having a different cross section;

[0019]FIG. 10 is an illustration of a packing similar to that of FIG. 7but having a different cross section;

[0020]FIG. 11 is an illustration of a packing similar to that of FIG. 7but having a different cross section;

[0021]FIG. 12 is an illustration of a packing similar to FIG. 7 buthaving a different cross section and having scrapers at the oppositeends thereof;

[0022]FIG. 13 is an enlargement of a portion FIG. 12; and

[0023]FIG. 14 is a view similar to FIG. 6 illustrating an embodiment ofthe invention wherein the hardfaced material is somewhat larger indiameter as compared with the diameter of the valve stem.

DETAILED DESCRIPTION

[0024] Referring now to the Drawings, and in particular to FIG. 1thereof, there is shown an improved valve 10 having a body 12constructed to provide a fluid path 14 and a body cavity 16. The fluidpath 14 is generally located in the lower end 18 of body 12, while thecavity 16 extends from the upper end 20 of body 12 to the location ofthe fluid path 14. Disposed within the fluid path 14 are seat ringrecesses 22 and seat rings 24 mounted in the seat ring recesses 22.

[0025] A valve member 28 is slidably positioned in the body 12 formovement through the cavity 16 such that sealing portions 30 of thevalve member 28 may engage the seats 24. The valve member 28 is operablyconnected to a valve stem 32 which extends through a stem packing 34located between the cavity 16 and a bonnet 35 mounted on the body 12.

[0026] The valve member 28 is actuated between the open and closedpositions by an actuating member 36. The improved valve 10 is in theopen position when the valve member does not engage the seats 24, and isin the closed position when the sealing portions 30 of the valve member28 engage the seats 24 thereby completely restricting the flow ofproduct P within the fluid path 14. The valve member 28 can be anymember used to restrict or close flow through the improved valve 10, butin the preferred embodiment the valve member 28 is a wedge.

[0027] As shown in FIG. 1, the actuating member 36 may comprise ahandwheel 38 secured to a threaded portion 41 of the valve stem 32. Thethreaded portion 41 is threadingly engaged with a nut 40 which issecured against rotation. As the handwheel 38 is turned clockwise, thenut 40 and the threaded portion 41 cause the valve member 28 to movedownward until the valve 10 is in the closed condition. If the handwheel38 is rotated counterclockwise, the nut 40 and the threaded portion 41effect opening the valve 10. Although not shown, other actuating memberswell known in the art are also within the scope of this invention.

[0028] As the valve member 28 is moved during the opening and closing ofthe valve 10, the valve stem 32 slidingly engages the stem packing 34.The stem packing 34 is installed such that when the valve stem 32slidingly engages the stem packing 34, a dynamic seal is effectivelyformed between the body 12, the bonnet 35, and the valve stem 32. Theseal contains the product P found within the piping system of which thevalve 10 is a part.

[0029] As the valve stem 32 moves up and down through stem packing 34,problems arise in the prior art because as the valve stem 32 ages,chemical corrosion from the product, galvanic corrosion from the stempacking 34, and both corrosion and erosion from the atmosphere cause anormal valve stem to lose the smoothness necessary to prevent damage tothe stem packing 34, which causes a leak path to form. Also, abrasivematerials accumulating between the packing and the stem can causescratching of the surface of the valve stem, also causing leak paths. Insevere cases, chemical and mechanical deterioration occur incombination.

[0030] As shown in FIG. 2, this problem is remedied by a thickness ofhardfaced material 42 on the section 43 of the outside diameter of thevalve stem 28 which slidably engages the stem packing 34. The hardfacedmaterial is a material resistant to corrosion, erosion, and scratchingand includes materials with Brinell hardness numbers ranging from 220 to380, such as Stoody® 6 manufactured by Stoody Company, 5557 NashvilleRoad, Bowling Green, Ky. 42101-7546, and Stellite® 6 and Stellite® 21manufactured by Deloro Stellite, Inc., 471 Dundas St. E. Belleville,Ontario, Canada K8N 1G2. Materials with Brinell hardness numbersapproximately 220 and below lack the required hardness to resistcorrosion, erosion or scratching, while materials with Brinell hardnessapproximately 380 and above create problems in the machining processbecause they are very hard to machine and cause maintenance problems forthe machining equipment. In the preferred embodiment, the hardfacematerial 42 comprises either Stellite® 6 or Stellite® 21 with a Brinellnumber range of 320-380.

[0031] For an existing valve stem, the hardfaced material 42 is placedon the valve stem 32 by the following process. First, the outsidediameter of an existing valve stem is machined down approximately 0.120inches using a conventional machine tool. Next, the outside diameter ofthe valve stem 32 is built back up using a gas metal arc welding (GMAW)process to produce a section of hardfaced material 42 having anapproximate total thickness of 0.200 to 0.250 inches. The now oversizedvalve stem 32 is machined back to its original diameter and may bepolished required by particular applications of the invention. In thepreferred embodiment using Stellite® 21, the finished valve stem 32 hasa section of hardfaced material 42 having a thickness of approximately0.090 inches. Other embodiments will call for a larger or smallerthickness ranging from 0.010 to 0.125 inches of hardfaced material 42.The exact thickness required for a particular application will dependupon the requirements of particular applications of the invention and/orby the corroded and scratched condition of the valve stem sought to befitted with the thickness of hardfaced material.

[0032] The hardfaced material may also be applied using the plasmatransfer arc (PTA) process. In the PTA process one or more powders,which may include metals and/or metallic salts and/or non-metallicmaterials, are directed into a plasma which melts the powdered materialprior to transfer to the surface being treated. The use of the PTAprocess to apply the hardfaced material is beneficial in that thecomposition of the hardfaced material can be matched to the requirementsof particular applications of the invention.

[0033] A new valve stem with a thickness of hardfaced material 42 andhaving a known diameter can be produced by the following method. First,a base material, such as stainless steel in the preferred embodiment, isforged or molded into a base stem having a diameter smaller than thenominal diameter, at least in the region that engages the packing. Themolding process can be done by any method known in the art for forging,casting and/or molding metal. The diameter of the base stem will usuallyrange between 0.010 to 0.125 inches smaller than the nominal diameter.In the preferred embodiment using Stellite® 6 or Stellite® 21, thediameter of the base stem will be 0.090 inches smaller than the knowndiameter. The diameter of the base stem can be varied according to therequirements of particular applications of the invention.

[0034] Once the base stem has been molded, hardfaced material 42, suchas that previously disclosed, is welded onto the base stem until thediameter is greater than the nominal diameter. This can be done by theuse of a gas metal arc welding (GMAW) process, providing an approximatetotal thickness of 0.125 to 0.250 inches of hardfaced material 42. Thenow oversized valve stem is machined back to its nominal diameter andpolished as In the preferred embodiment using Stellite® 6 or Stellite®21, the finished valve stem has a thickness of hardfaced material ofapproximately 0.090 inches. Other embodiments will call for a larger orsmaller thickness ranging from about 0.010 inches to about 0.125 inchesof hardfaced material. The exact thickness required for a particularapplication will be dictated by the requirements of particularapplications of the invention.

[0035] The hardfaced material may also be applied using the plasmatransfer arc (PTA) process. In the PTA process one or more powders,which may include metals and/or metallic salts and/or non-metallicmaterials, are directed into a plasma which melts the powdered materialprior to transfer to the surface being treated. The use of the PTAprocess to apply the hardfaced material is beneficial in that thecomposition of the hardfaced material can be matched to the requirementsof particular applications of the invention.

[0036] Referring to FIGS. 4, 5, and 6, the method of the presentinvention is illustrated. A valve stem 44 is provided with a portion 46having a reduced diameter relative to the nominal diameter 48 of thevalve stem. The reduced diameter portion comprises the area of the valvestem 44 which engages the seal of the valve. The reduced diameterportion 46 may be provided either in the original manufacture of thevalve stem 44, or by grinding or otherwise machining a preexisting valvestem to provide the reduced diameter portion 46.

[0037] The reduced diameter portion 46 is filled with a layer ofhardfaced material 50 which is applied to and secured to the valve stem44 by welding. The welding of the hardfaced material 50 continues untilthe outer surface 52 thereof extends beyond the nominal diameter 48 ofthe valve stem 44. Thereafter, the hardfaced material is ground andpolished to provide an exterior surface 54 thereof which is coincidentwith the nominal diameter 48 of the valve stem 44.

[0038] As is shown in FIG. 14, the hardfaced material 15 may have anoutside diameter which is somewhat larger than the outside diameter ofthe valve stem 44, it being understood that the extent to which theoutside diameter of the hardfaced material 50 exceeds the outsidediameter of the valve stem 44 is exaggerated in FIG. 14 for clarity. Inactual practice the extent to which the outside diameter of thehardfaced material exceeds the outside diameter of the valve stem doesnot exceed about 0.010 inches, it being understood that the diameters ofthe hardfaced material and of the valve stem can be varied in accordancewith the requirements of particular applications of the invention. Theembodiment of the invention illustrated in FIG. 14 is applicable both toremanufactured valve stems and to newly manufactured valve stems.

[0039] Referring now to FIG. 7, there is shown an improved packingconstruction 60 useful in conjunction with the improved valveillustrated in FIGS. 1-6, inclusive, and described hereinabove inconjunction therewith. A valve assembly 62 includes a valve stem 64which is provided with a section of hardfaced material 66 which isconstructed as described hereinabove in conjunction with FIGS. 1-6,inclusive. The improved valve packing 60 is aligned with the section ofhardfaced material 66.

[0040] The improved valve packing 60 comprises a vertically stackedarray of metal pressure rings 68. Between each of the metal pressurerings 68 there is positioned a graphite seal 70. Both the metal pressurerings 68 and the graphite seals 70 have an inverted-V or chevron shapein cross section. Other cross sectional configurations of the metalpressure rings 68 and the graphite seals 70 can be used in the practiceof the invention, if desired.

[0041] Beneath the lower most graphite seal 70 there is provided afemale adapter 72. Above the upper most graphite seal 70 there is aprovided a male adapter 74. A follower 76 is positioned above the maleadapter 74.

[0042] As will be appreciated by those skilled in the art, the femaleadapter 72, the male adapter 74, and the follower 76 comprise componentswhich are well known in the valve industry. In a typical application,the male adapter 74, the follower 76, an associated gland, and eye-boltsare employed to impose downward pressure on the packing which surroundsa valve stem. The object is to close any leak paths which mightotherwise exist through the packing, thereby preventing fugitiveemissions.

[0043] As is also well known, rubber impregnated fabrics, rubber coatedfabrics, plastic impregnated fabrics, plastic coated fabrics, rubber andrubber-like compositions, plastic compositions, graphite, and othermaterials have heretofore been utilized as valve stem packings.Typically, such materials are arranged in layers, with each layercomprising an inverted V-shaped or chevron configuration.

[0044] In the use prior art packing constructions, the compressive forceimposed by the eye-bolts, the gland, the follower, and the male adapterhave resulted in significant compression of the uppermost layers of thepacking. However, the lower layers comprising the packing have remaineduncompressed. This results in leak paths through the lower portion ofthe packing, which in turn leads to fugitive emissions from the valve.

[0045] In direct contrast to the unsatisfactory functioning of prior artpacking constructions, in the use of the packing of the presentinvention the application of compressive force by the actuation ofeye-bolts or other threaded members, the associated gland, the follower,and the male adapter initially causes compression of the uppermostgraphite seal 70. The material comprising the uppermost graphite seal 70is thereby forced outwardly from the space between the male adapter andthe uppermost metal pressure ring 68. Inward and outward flow of thematerial comprising the upper most graphite seal 70 continues until themale adapter engages the upper most metal pressure ring 68. Thereafterthe process repeats itself except that the outward flow comprises thematerial of the next succeeding graphite seal 70. Again, outward flow ofthe material comprising the next succeeding graphite seal 70 continuesuntil the upper most metal pressure ring 68 engages the next succeedingmetal pressure ring 68. Thereafter the process continues except that theoutward flow comprises the material of the succeeding graphite seal 70,etc.

[0046] In this manner the material comprising each and every one of thegraphite seals 70 is cause to flow inwardly and outwardly, therebyentirely filling the spaces between the packing and the valve stem, andbetween the packing and the valve body. In this manner, any possibilityof a leak path through the packing is completely eliminated, the endresult being complete elimination of the problem of fugitive emissionsfrom valves incorporating the present invention.

[0047]FIGS. 9, 10, and 11 illustrate alternative cross sectionalconfigurations of the metal pressure rings and the graphite seals of theimproved packing of the present invention.

[0048] It will be appreciated that the component parts of the apparatusillustrated in FIG. 7 other than the improved valve packing 60 areidentical to the component parts of the apparatus illustrated in FIG. 1.In FIG. 8 there is shown an apparatus 80 comprising numerous componentparts which are identical to component parts of the apparatus shown inFIG. 7. Such identical component parts are identified in FIG. 8 with thesame reference numerals utilized hereinabove in the description of theapparatus of FIG. 7.

[0049] The apparatus 80 includes a bonnet 82. The follower 76 of theimproved valve packing 60 extends above the upper end of the bonnet 80.Otherwise, the apparatus of FIG. 8 is identical to the apparatus of FIG.7 in construction and operation.

[0050]FIGS. 12 and 13 illustrate an improved packing construction 90which differs somewhat from the packing construction 60 illustrated inFIGS. 7-11, inclusive, and described hereinabove in conjunctiontherewith. The packing 90 includes graphite seals 92 and pressure rings94. The packing 90 further includes thrust plates 96 located at theopposite ends thereof and scrapers 98. The packing 90 is mounted in abonnet 100 and is engaged by a follower 102 at the upper end thereof.

[0051] In use, the packing 90 functions similarly to the functioning ofthe packing 60 as described hereinabove. The scrapers 98 prevent debris,that may accumulate on the valve stem either above or below the packing90, from becoming lodged in the graphite seals 92 which, if allowed tooccur, could lead to deterioration either of the graphite seals or ofthe valve stem which in turn could lead to leak paths through thepacking 90. As will be appreciated by those skilled in the art, thecross sectional configurations of the pressure rings and graphite sealsillustrated in FIGS. 8, 9, 10, and 11 may be utilized in the packingmember 90 depending upon the requirements of particular applications ofthe invention. Likewise, the cross sectional configuration of thegraphite seals and the pressure ring of the packing 90 as illustrated inFIGS. 12 and 13 may be utilized in the packing 60, if desired.

[0052] Although preferred embodiments of the invention are illustratedin the accompanying Drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe embodiments disclosed, but is capable of numerous rearrangements,modifications, and substitutions of parts and elements without departingfrom the spirit of the invention.

I claim:
 1. In a valve of the type including: a. a body constructed tohave (i) a fluid path; (ii) a stem bore connected in fluid communicationwith the fluid path; and (iii) a seat; b. a stem packing located in thestem bore; c. a valve member having a valve stem and a sealing member,the valve member being positionable in the stem bore so that the sealingmember may engage the seat, the valve stem engaging the stem packing inthe stem bore, the valve stem made of a base material; and d. anactuating member connected to the valve stem for actuating the valvemember; the improvement comprising: the valve stem including a reduceddiameter recessed section aligned with the stem packing and a section ofwelded hardfaced material filling the reduced diameter recessed section,having a thickness of between about 0.010 inches and about 0.125 inchesthereby preventing damage to the hardfaced material under the action offoreign materials in the stem packing, and having a Brinell hardnessnumber of between about 220 and about 380 in contact with said stempacking so that upon relative movement between the valve stem and thestem packing the welded hardfaced material filling the reduced diameterrecessed section of the valve stem resists corrosion, erosion, andscratching due to foreign materials in the stem packing over a prolongedperiod of time; and an improved stem packing located in the stem bore inengagement with the hardfaced material and comprising at least one metalpressure ring and at least one sealing member.
 2. The improvementaccording to claim 1 wherein sealing member of the improved stem packingcomprising a graphite seal.
 3. The improvement according to claim 2further characterized by a plurality of metal pressure rings arranged ina vertically stacked array and a plurality of graphite seals, each ofthe graphite seals being positioned between two of the metal pressurerings comprising the array.
 4. The improvement according to claim 3wherein each of the metal pressure rings and each of the graphite sealsis chevron shaped in cross section.
 5. The improvement according toclaim 3 wherein each of the metal pressure rings and each of thegraphite seals have the cross sectional configuration illustrated inFIG.
 9. 6. The improvement according to claim 3 wherein each of themetal pressure rings and each of the graphite seals have the crosssectional configuration illustrated in FIG.
 10. 7. The improvementaccording to claim 3 wherein each of the metal pressure rings and eachof the graphite seals have the cross sectional configuration illustratedin FIG.
 11. 8. The improvement according to claim 3 wherein each of themetal pressure rings and each of the graphite seals have the crosssectional configuration illustrated in FIG.
 12. 9. The improvementaccording to claim 3 further characterized by scrapers located at theopposite ends of the stacked array for engagement with the valve stem toprevent debris from entering the packing member.
 10. The improvementaccording to claim 9 further including thrust plates positioned on theopposite sides of the packing members.
 11. In a valve having a bodyconstructed having a fluid path, a stem bore and a seat, a valve memberhaving a valve stem and a sealing member, said valve member beingpositionable in said stem bore so that said sealing member may engagesaid seat, said valve stem engaging stem packing located between saidvalve stem and said stem bore, and an actuating member connected to saidvalve member wherein the improvement comprises: said valve stemcomprising a recessed portion aligned with the stem packing, saidrecessed portion being filled with a weldment of hardfaced materialselected from the group consisting of one or more materials havingBrinell hardness numbers of between about 220 and about 380, said weldedhardfaced material having a thickness of between about 0.010 inches andabout 0.125 inches thereby preventing damage to the hardfaced materialdue to foreign material in the stem packing over a prolonged period oftime; said stem engaging packing comprising at least one metal pressurering and at least one sealing member.
 12. The improvement according toclaim 11 wherein sealing member of the improved stem packing comprises agraphite seal.
 13. The improvement according to claim 11 furthercharacterized by a plurality of metal pressure rings arranged in avertically stacked array and a plurality of graphite seals, each of thegraphite seals being positioned between two of the metal pressure ringscomprising the array.
 14. The improvement according to claim 13 whereineach of the metal pressure rings and each of the graphite seals ischevron shaped in cross section.
 15. The improvement according to claim13 wherein each of the metal pressure rings and each of the graphiteseals have the cross sectional configuration illustrated in FIG.
 9. 16.The improvement according to claim 13 wherein each of the metal pressurerings and each of the graphite seals have the cross sectionalconfiguration illustrated in FIG.
 10. 17. The improvement according toclaim 13 wherein each of the metal pressure rings and each of thegraphite seals have the cross sectional configuration illustrated inFIG.
 11. 18. The improvement according to claim 13 wherein each of themetal pressure rings and each of the graphite seals have the crosssectional configuration illustrated in FIG.
 12. 19. The improvementaccording to claim 13 further characterized by scrapers located at theopposite ends of the stacked array for engagement with the valve stem toprevent debris from entering the packing member.
 20. The improvementaccording to claim 19 further including thrust plates positioned on theopposite sides of the packing members.